I second what Brian said above.
My guess is that youre asking us why your AC belt disappeared?
The same happened to me when the idler pulley, which the belt goes around at the bottom, seized up. In your case, it could also be a seized compressor, which gets expensive. The pulley is easy to remove and replace, and the part is cheap (
http://www.everythinginfiniti.com).
Dennis (Q45tech), if I recall accurately, says compressor failure is caused by a failure to reoil and flush the system regularly.
Get under the car and look at the pulley at the bottom and see if it rotates, or if its frozen. If you get one pulley replaced, it would be wise to do all three at the same time.
I once let a water pump/power steering pulley fail, at which point the belt snapped off, my power steering died, and my motor overheated briefly -- left me stranded in a parking lot at 2am. A seized pulley worth a few bucks could have resulted in thousands of dollars in damage, but I was lucky.
-Jesda